Conventional methods for imparting kinetic energy in and/or displacing a body over a large distance include the release of stored energy, such as in stretched elastomeric bands, compressed springs, pyrotechnics, and the like, and the performance of work by electromechanical and electrohydraulic drives. These methods, however, present various limitations and concerns, including, for example, those relating to mass, packaging, complexity, and robustness.
Currently, active-material based actuators, including those comprising SMA wires, cables, bars, etc., are used to directly drive a body, or release a holding mechanism so as to allow stored energy to act upon the body. Whereas SMA actuators address the afore-mentioned concerns, they are currently limited to providing at most 8% displacement (i.e. 8% of their length) in a single actuation cycle. To achieve large displacements requires a large linear length of SMA material, which in many applications is prohibitive due to packaging considerations. As such, in order to achieve displacements greater than that which is allowed by the wire length, complex transmissions and/or amplifying mechanisms, including gears, levers, pulleys, and the like, have been employed. However, the inclusion of these measures re-introduces at least some of the afore-mentioned concerns.